The present invention relates to a method and apparatus for air classifying or separating the lamina and stern of threshed tobacco leaves by passing a mixture of tobacco leaf particles through an upwardly moving air stream to carry the light particles upwardly, while allowing the heavy particles to fall downwardly.
In the processing of leaf tobacco into a state suitable for use in the manufacture of tobacco products, e.g., cigarettes, it is necessary to separate the lamina from the stem in the leaf structure. After separation, these elements are separately treated before use. This separation is normally accomplished by first threshing the tobacco, i.e., cutting or tearing the lamina from the leaf stem. As used herein, the term "stem" includes both the main stem and side veins of the tobacco leaf. The resultant mixture of lamina and stem pieces is fed to an air separator or classifier to segregate the lamina pieces from the stem pieces.
In an air separator, air is blown upwardly from the lower part of a chamber into contact with the leaf mixture, which is projected across the chamber substantially perpendicular to the direction of the air stream. Since lamina particles have a larger surface area to weight ratio than stein particles, the air stream exerts a relatively greater lift on the lamina particles. The velocity of the air stream is adjusted so that the lamina particles are carried upwardly and out of an exit opening near the top of the chamber, while the stein particles fall to the bottom of the chamber, where they are removed through a lower opening. Thus, lamina and stem particles are separated.
Unfortunately, this separation process does not operate with complete efficiency, and some lamina particles, especially if they are still attached to small pieces of stern, are not separated from the stem particles. To achieve more complete separation, air separators have been modified so that the residual leaf mixture, i.e., material not discharged as lamina, is again subjected to an air stream. One way to achieve this additional separation is to again pass the leaf mixture through the air stream in the same chamber, e.g., by redirecting the leaf mixture back across the chamber through the air stream.
An example of a multi-pass separator is found in U.S. Pat. No. 4,465,194 to Coleman, which discloses a tobacco leaf separator having a primary chamber and a secondary chamber. The primary chamber has a rear wall, a front wall, and a lamina discharge port at the top of the chamber. An air-permeable conveyor extends from the rear wall of the chamber to the front wall. A tobacco inlet including a first winnower is positioned in the rear wall above the conveyor. A second winnower is positioned adjacent the front wall above the conveyor, below the level of the first winnower.
In the operation of the Coleman apparatus, a mixture of lamina and stem is introduced into the primary chamber through the tobacco inlet and projected to the front wall of the chamber by the first winnower. An air stream is conveyed through the permeable conveyor, upwardly through the primary chamber, and out the lamina discharge port. Lighter lamina is carded by the air stream upwardly through the discharge port. Material striking the front wall drops onto the second winnower which rotates away from the front wall to project the collected particles from the top of the winnower back across the separation chamber, again subjecting the particles to the air stream to separate lighter particles from heavier particles. Particles on the conveyor belt are conveyed into the secondary chamber, where they are once again subjected to the air stream to carry lighter particles up to the lamina discharge port. Heavier particles drop into a stem discharge opening.
Another example of a multi-pass separator is found in U.S. Pat. No. 4,701,256 to Cross, Jr. which describes a separator having a tobacco inlet with a winnower in a back wall, an inclined air-permeable ramp extending from a front wall toward the back wall, and an air impeller located at the top of the ramp adjacent the front wall, at a level below the plane of the tobacco inlet. In operation, air is conveyed upwardly through the inclined ramp and the separation chamber, and tobacco is propelled across the chamber from the tobacco inlet. Lighter particles are conveyed by the air stream out of the top of the chamber, while heavier particles strike the front wall and fall to the air impeller, which propels these latter particles outwardly across the chamber, and again into the air stream for separation.
U.S. Pat. No. 4,475,562 to Thatcher et al describes a tobacco separator having a tobacco inlet in one wall, and an air inlet communicating with a source of air positioned in the separator wall opposite the tobacco inlet and beneath the horizontal plane of the tobacco inlet. A downwardly and inwardly projecting member extends from the separator wall above the air inlet opposite the tobacco inlet. In operation, tobacco is projected upwardly into the chamber from the tobacco inlet and air is introduced into the chamber upwardly from the air inlet. The tobacco stream is contacted by the air stream, which separates the tobacco into a lighter fraction which is carded upwardly in the chamber and out of the lamina outlet, while the heavier tobacco fraction, a portion of which strikes the opposite wall, drops downwardly onto the inclined member. From there, the heavier fraction falls from the lower end of the inclined member, and is again subjected to the force of the air stream to again effect separation. Finally, the heavier fraction drops to the bottom of the chamber for collection. The lamina fraction is conveyed to another separator.
The leaf mixture may also be subjected to an additional separation by discharging the tobacco particles from the first chamber into one or more additional chambers having a similar configuration. For example, U.S. Pat. Nos. 5,099,863 to Coleman and 5,325,875 to Coleman et at, describe a system comprised of a plurality of air separators connected in a front-to-back relationship. Each separator includes a back wall, a front wall, and a lamina receiving and discharge means positioned in the top of the separator. A conveyor belt is positioned in the bottom of the chamber, inclining upwardly from the back wall to the front wall. A tobacco inlet port containing a winnower is positioned in the back wall of the separator adjacent the conveyor.
In operation, air is projected upwardly through the conveyor and the separator chamber, and tobacco is discharged upwardly into the conveyor from the tobacco inlet port. Lighter particles are conveyed by the air upwardly in the chamber where they are received and discharged, while heavier particles are conveyed by the conveyor to a discharge port, which also serves as the tobacco inlet port for the adjacent downstream separator which is of a similar construction.
The above U.S. Pat. No. 5,325,875 to Coleman et al also describes a series of front-to-back separators, each of which, except for the last separator, have a first winnower located in the back wall above the conveyor, and a second winnower located adjacent the front wall above the conveyor, but below the level of the first winnower. A tobacco discharge port is located in the front wall of the separator above the second winnower and approximately on a horizontal plane with the first winnower. This tobacco discharge port also serves as the tobacco inlet for a second separator of similar construction. The discharge port of the second separator serves as the inlet port for a third separator of similar construction, except that the discharge port of the third separator is at the bottom of the separator beneath the end of the conveyor. A common conveyor extends beneath all three separators.
In operation, tobacco entering the first separator is separated by the air stream, with the lightest lamina being carded by the air stream to the top of the separator and the heaviest particles falling onto the conveyor. Particles of intermediate density are projected directly across the separator and into the tobacco outlet for further treatment in the second separator, while another portion drops onto the second winnower, which propels the particles back into the air stream from the top of the second winnower for additional separation. This process is repeated in the second separator, and in the third separator, except for the fact that all intermediate particles fall onto the second winnower in the third separator. Importantly, only the middle portion of the tobacco mixture is conveyed to the next separator, while the heavier portion, which my also contain lamina, receives no further treatment.
Another air separation system comprised of a plurality of air separators in series connected by a common conveyor is described in U.S. Pat. No. 5,205,415 to Surtees. In each separator, tobacco is projected across the separation chamber from a tobacco inlet in the rear wall and air is directed upwardly into the chamber through the conveyor belt. The tobacco is separated into a light fraction which is carried out the top of the separation chamber, a heavy fraction which falls onto the conveyor, and an intermediate fraction which is carded across the separator chamber and out a discharge port that forms the tobacco inlet port of the next separator.
An air separation system combining the multi-pass separation of a single chamber with the separation achieved by passing the tobacco mixture through a plurality of front-to-back chambers would provide even greater separation efficiency. However, connecting multi-pass separators together so that all of the non-lamina material is conveyed to a second separator has not proved to be practical. In air separators, at least a part of the leaf mixture, i.e., the leaf material remaining after separation of lamina, is collected adjacent the bottom of the separator chamber. In order to treat this material in a second separator, the material must be introduced into the second separator at a level which is above the level of the discharge point in the first separator.
Theoretically, the discharge outlet of the first separator could be connected to the inlet of the second separator by a conduit. Movement of lamina through a conduit, however, causes breakage or degradation of the lamina, decreasing its usefulness. Thus, this approach is not practical. It would also be theoretically possible to simply raise the first separator to a height where the discharge outlet of the first separator was at a level with the inlet of the second separator. The discharge, and intake ports could then be connected without the need for a conduit.
Conventional separators, however, are quite large, normally having a height of over 13 feet above floor level. The normal vertical distance between the discharge port and the intake port is almost 8 feet. Therefore, it would be necessary to raise the first separator about 8 feet about floor level, resulting in the top of the first separator being about 21 feet about the floor. Not only would the operator have to climb to this height to observe the interior of the first separator and make any alterations in its set-up, which would be time-consuming and possibly dangerous, but existing processing facilities simply do not have ceiling which are this high. Thus, if this system was to be installed in an existing processing facility, it would be necessary to raise ceiling heights, resulting in considerable cost, as would the heating or cooling of the additional space.
An air separator in which a mixture of tobacco leaf lamina and stem could be subjected to multiple exposures to an air stream in a treatment chamber, and which could be connected in series to a similarly constructed separators without a conduit so that all residual leaf mixture could be subjected to air streams in multiple chambers would be of great value in the pertinent industry. An air separator of this construction that could be installed in existing processing facilities would be of particular value.
Thus, one aspect of the present invention is to provide an improved air separator in which a mixture of tobacco leaf lamina and stein is subjected to multiple passes through an upwardly moving air stream to discharge lamina from the upper part of the separator and all non-lamina material from adjacent the bottom of the separator, directly into the intake of a second separator.
Another aspect of the present invention is to provide a series of milti-pass air separators in which the leaf mixture discharge outlet of one separator is directly connected to the leaf mixture intake of a second separator, with the series of separators being of a height such that they can be installed in a existing processing facility.
Still another aspect of the present invention is to provide a method for subjecting a mixture of tobacco leaf lamina and stem to multiple separations in a single chamber, and separations in a plurality of air separator chambers.
These and other aspects of the present invention will be obvious to one skilled in the art upon a reading of the Summary of the Invention and the Detailed Description of the Invention which follow.